Selsyn controlled electric motor system



y 1947. M. A. EDWARDS 2,424,809

SELSYN' CONTROLLED ELECTRIC MOTOR SYSTEM Filed. Oct. 17, 1940 I Inventor: Martin A. Edwards,

70 d. M b5 Hig zttorney Patented July 29, 1947 2,424,609 8mm conrnoram suic'rmc Moron srs'rau mamsmiaxnsumsrto General Electric New York Company, a corporation of Application October 17, 1.4., Serial No. 361,599

a Claim. (or. 172-289) This invention relates to control systems. more particularly to follow-up control systems for driving an object into positional agreement with a pilot device. and it has for an object the provision of a simple, reliable and improved system of this character.

More specifically, the invention relates to fol-- low-up systems in which fine and coarse controlling means are employed for controlling the driving means which drives the driven oblect, and a specific object of the invention is the provision of improved means for transferring th'e control from the fine controlling means to the coarse controlling means when the positional disagreement of the pilot device and driven object exceeds a predetermined amount. and for re-- transferring the control to the fine controlling means when the positional disagreement becomes less than this predetermined amount. r

In carrying the invention into eflect in one form thereof, means are providedfor driving the.

driven object, and coarse and fine control means responsive to positional disagreement oi the: pilot device and driven object to ether with connections between the coarse and fine control means and the driving means are provided for controlling the driving means to drive the driven obiect toward correspondence with the pilot device. The coarse control means are normally ineffective when the positional disagreement between the pilot device and driven object is less than a predetermined amount, and electric-valve means ining of the invention, reference should now be had to the following specification and to the accompanying drawing in which Fig. l is a simple, diagrammatical representation of an embodiment "of the invention, and Fig. 2 is a simple, diagrammatical representation of a modification.

Referring now to the drawing. an object it is to be driven in positional agreement with a pilot or control device II by suitable driving means such. for example, as represented by the direct current motor I: to the drive shaft of which the object It is connected by means of suitable reduction gearing (not shown). Direct current is supplied to the armature oi the motor l2 by means of aspeoial generator ll having a pair of short circuited armature'brushes its and a pair or load brushes its to which the armature of th'e'motor i2 is connected by means of conductors ils. The generator II is an armature. '20 reaction excited dynamoelectric machine and is driven at a speed which is preferably substantially constant by any suitable driving means, such as an induction motor It to the drlve'shaft of which the shaft of the armature reaction ma- 26 chine II is connected by suitable coupling means (not shown) The axis of the flux which is produced by the short circuited armature brushes I3. is referred to u the short circuit axis, and the axis which is displaced 90 electrical degrees sofrom the short circuit axis is referred to as the cluded in the connections between. the I control means and the driving means serve 'to" render th'e coarse control means eifective and thereby to transfer the control from the fine control means to the coarse control means when the positional disagreement exceeds the predetermined amount mentioned in the foregoing, and to render the coarse control means ineffec- In illustrating the invention in one form thereof, it is shown as applied to a follow-up control system in which the drivenobiect is driven by an electric motor, but it will be understood that it may be applied to follow-up systemsin; which the driven object is driven by any other control axis. If it be assumed that the axis of the brushes II. coincides with the short circuit fiux axis, then the load brushes lls are on the control axis. The net fiux along the control axis is produced by two opposing control iield windings its and lid, a series compensating field winding l3. and the armature reaction of the load current itself. The fiux along the short circult axis of the dynamoelectric machine It is J 49 produced by the shunt field winding l3: and the tive when the disagreement becomes less than the predetermined amount.

armature reaction of the short circuit current. This short circuit axis flux generates the voltage which appears across the load brushes l3, and the control axis fiux produces the voltage 46- which appears across the short circuited brushes its and causes short circuit current to fiow.

The operationof the machine It will be readily understood by considering the operation with only one control field winding, for example, the field winding its. and also without the shunt 3 field winding I3 and the series compensating winding l3e, and then subsequently considering the effect of these field windings on the operation.

Let it be assumed that voltage is applied to the field winding '30 and current begins to build up in this field winding. Immediately there is generated a voltage in the short circuit path which circulates a large current in the short circuit.

Since the resistance of the short circuit is so low as to be almost negligible, the control field winding 3c is only required to produce a very small fiux in order to produce a large current in the short circuit and a correspondingly large armature fiux. Furthermore, since the flux of the control field winding need only build up to such a low value, and since the reactance oi the short circuited armature is very low, full load current in the short circuit will be obtained in an exceptionally short'time. The armaturereaction fiux produced by the short circuit current generates a voltage across the load brushesllb and causes load current to flow. This load current will produce an armature flux which opposes the flux of the control field winding Us. This would, of course, mean that the flux of the control field winding 3c would have to be large enough to overpower this control axis armature flux. However, by using the series compensating field winding is through which the load current passes, the armature reaction on the control axis can be substantially completely neutralized. Thus, by the use of this series compensating held, the control field is only required to produce enough field flux and voltage to overpower the resistance drop in the short circuit; and the time constant or rate of response the machine is consequently very fast. a

The function of the shunt field'winding II: is to reduce the steady state short circuit current. For any given voltage across the load brushes Be, there must be a corresponding flux on the short circuit axis. If any part of this flux is produced by a shunt field winding, the amount oi flux which must be produced by the short circuit armature current will be correspondingly reduced. For example, if the shunt field is adjusted to give enough excitation to generate ninetenths of the voltage across the load brushes "a, the short circuit current for any given load voltage need be only one-tenth as great as it would have to be if there were no shunt field winding.

The control field windings He and I34 on the control axis of the armature reaction generator l3 are connected in the cathode-anode circuits of electric valves i5 and I8, respectively. The cathode-anode circuits oi. these valves II and II are connected across a suitable source of direct current voltage I! with the anodes o! the valves I5 and I5 connected through the control field windings I30 and He, respectively, to the positive side of the source i1, and the cathodes or these valves connected through the self-biasing resistor I 8 to the negative side of the source I]. The cathode grid circuit of the valve ll extends from the cathode of the valve through the selfbiasing resistor l8 and the resistor is to the grid 4 of conducting paths is provided for controlling the grid voltage of the valves l5 and ii. The anode-cathode circuit of the valve ii is connected across the secondary winding 22- or a transformer 12 whose primary winding 22s is connected across a suitable source of single-phase alternating voltage represented by the two supply lines 28. As shown, the anodes II. and 2h, 0! this valve are connected through resistors 19 and II, respectively, to one terminal of the secondary winding 22., and the cathodes e and Ila are connected through a biasing resistor 24 to the opposite terminal of the secondary winding 22a. Since the valve 21 has two anodes, it has two conducting paths and the current in each of these paths is separately controllable by controlling the voltages applied to the two grid control elements II. and Ilr. The grid 2|. controls the flow of current in the path between the cathode Ile and the anode 2|, and the grid 2i! controls the conductivity of the path between the cathode Ila and the anode lit. The cathode grid circuit for the left-hand conducting path of the valve 2| extends from the cathode through the biasing resistor 24, the left-hand portion oi a resistor ii, and a secondary winding 26. of a transformer to the grid 2 I, and similarly, the cathode grid circuit for the right-hand conducting path of the valve 2| extends from the cathode through biasing resistor 24 and the right-hand path of resistor II and secondary winding 28b of transformer I. to the grid 2h. The voltages of the grids II- and 2h with respect to the cathodes lie and lid, respectively, as a result of the inclusion of the biasing resistor 24 in the anodecathode circuits of valve ii are such that both paths of the valve 2| normally conduct equal amounts of current, for example, 4 milliamperes. This condition of equal conduction in both paths of the valve ll occurs when the follow-up system is in correspondence, 1. e., when the driven object II is in positional agreement with the pilot device II. when equal amounts of current are flowing through both paths of the valve II, the voltage drops across resistors II and 20 are equal and these voltage drops .combined with the voltage drop across resistor ll produce a bias 0! the voltages of the grids of valves II and IS with respect to their cathodes such that these valves conduct equal amounts of current, e. g., 40 milliamperes. The current conducted by the valves l5 and i6 excite the control field windings He and I34 0! the armature reaction generator l3. However, since the control field windings its and its act in opposition to each other, the net exciting fiux along the control axis of the generator II is zero and therefore the voltage at the load brushes lie is zero. It will thus be clear from the loreloing that when the follow-up system is in correspondence, equal. amounts of current fiow in both paths of the valve Ii and likewise equal amounts 0! current flow in the valves I5 and IS, with the of the valve and as a result, the grid is given a 1 negative bias. Similarly, the cathode grid circuit of valve I6 extends from the cathode through biasing resistor l8 and resistor 20 to the grid of valve l6, and accordingly, the grid of this valve is similarly given a negative bias. 1

A twin triode electric valve 2! having a pair result that the terminal output voltage of the generator II is zero.

In order to vary the bias voltages of the grids I I. and 2|: 0! the valve ii, a component voltage of variable magnitude is supplied to the grid circuit substantially in phase with the anode volt- .age through the transformer 2', whose secondary windings I. and "a are connected in the cathode grid circuits oi the valve II as explained in the foregoing, and whose primary winding is connected to the single-phase alternating current source II through rotary induction apparatus 11- lustrateh as comprising a rotary induction de- .apparatus which, in turn, 'tion in the relationship of the currents iiowing in the conducting paths of the valve 2|. The

' for example, the ratio gearing between sumed, then for each 5 Vice :1 referred to as the transmitter and a similar rotary induction device 28 referred to as the receiver regulator. The rotary induction device 21 comprises a rotor member 21- provided with a single-phase winding (not shown) and a stator member 21 provided with a distributed three-element winding (not shown) that is physicallysimilar to the polyphase winding 0! an ordinarywound rotor induction motor." The'stator and rotor windings are arranged in inductive relationship with each other so that the alternating magnetic field due to the current flowing in the primary winding induces voltages in the elements of the secondary winding. The receiver-regulator 28 is in all respects identical with the transmitter 21, and the terminals of its stator winding are connected to the terminals of the stator winding of the transmitter by means of conductors 29 so that the voltages induced in the stator winding of .the transmitter cause currents to flow in the stator winding of the receiver regulator, thereby producing a magnetic field similar to the magnetic field produced by the current flowing in the rotor winding of the transmitter.- Rotation o. the rotor member or the transmitter causes a voltage to be induced in the rotor winding of the receiver owing to the shift in the position of the axis oi the magnetic field of the receiver regulator relative to theaxis oi the coil of the rotor member, and themagnitude oi! this induced voltage depends upon the relationship of the axis of this winding to the axis of the magnetic field, e. g., when the axes of the magnetic field and of the rotor winding are parallel, the induced voltage is maximum, whereas when these axes are at, right angles with each other, the induced voltage is zero. It will therefore be clear that rotation of the rotor of the transmitter or of the receiver regulator will vary the magnitude or the component voltage supplied to the grid circuit of the electric valve will result in a variagrid connections to the electric valve 2| are so made, as explained in the ioregoing, that when.

the voltage applied to one of the valve 2| is increased, the voltage applied to the grids of the simultaneously dewhen the current other grid of the valve 2| is creased and consequently,

through one of the conducting paths or the valve 2| is increased, the current-through the other conducting path is simultaneously decreased.

The rotor of the transmitter 21 is mechanically connected through suitable gearinginot'shown) to the movable element of the pilot" device II. For the purpose of increasing the accuracy and sensitivity of the control, the ratio of this gearing between the pilot device and the rotor of the transmitter can be made as large as is desired, may be as great as 72:1, i. e., for each degree that the pilot device is rotated, the rotor of the transmitter is rotated 72. The rotor of the receiver regulator 28 is connected either to the shaft of the motor II or to the shaft of the driven object In by means of suitable gearing (not shown) having the same ratio as the the pilot device and the transmitter. i

This large gear ratio provides a very fine and very accurate control. It the ratio is 72: 1 as asof rotation oi the pilot device the rotor of, the transmitter 21 is rotated a full 360. However, since the axes of therotor winding of the receiver regulator 22 and the magnetic field of the stator are parallel at two points in one complete revolution of the transmitter, i. e,, at 0 revolution and at 180 revolution of the transmitter, it-will be clearthat the pilot device I valve becomes conducting.

al disagreement equals or exceed this predeter- "valve 2| through electric valves 33 and and the driven object must notbe allowed to become more than 2 /2" out oi! correspondence with each other while under the control of the'high speed line. control system because when .this amount of positional disagreement occurs, the same relationship exists between the rotors of the transmitter and receiver regulator as .exists when the pilot device and driven object are in correspondence with each other.. In practice, under actual operating conditions, the, rotor. of the transmitter often does become more than this amount out 0! correspondence with thedriven object iii and a coarser-system is therefore provided for taking over the control from the high speed line control system before this amount oi positional disagreement is exceeded; This coarse system is illustrated as comprising a transmitter 30 that is identical with the transmitter 21 and a receiver regulator 3| that is similar to the receiver regulator 28. The singlephase rotor winding of the transmitter 30 is connectedto the alternating voltage source 21, and the single-phase rotor winding of the receiver regulator ii is connected to the termlnalsot the primary winding 32. o! a transformer 82, the terminals of the secondary winding 32b of which are connected to the grids 2|. and 2|: of the 34. The midpoint of this secondary winding up is connected to the midpoint o! the resistor 25.. The stator windings oi the transmitter 30 and receiver regulator II are connected to each other by means of conductors 35.

The rotor of the transmitter is directly connected to the rotatable member oi-the pilot device by means of suitablegearing having a 1:1 ratio, andthe rotor member of the receiver resulator 3| is connected through suitable gearing (not shown) having a 1:1 ratio to the driven ob- .Ject l0.

Thus it will be seen that the transmitter 30 and the receiverregulatorll constitute a low speed system and provide the desired coarse control.

The electric valves 33 and 34 may be or any suitable type but are preferably of the two-electrode type into the envelopes or which a small quantity or an inert gas; such for example as neon, is introduced after exhaust. 'A characteristic of a valve of this character is that when a voltage of less than a predetermined value is applied to its terminals, the valve does not conduct current and that when this voltage isexceeded, the neon gas becomes ionized and the The transformer 32 is so designed that when the'positional disagreement oi the pilot device anddriven object is less than a predetermined 2 /2 or less, the voltage applied to valves 33 and 3415 less than the ionization or breakdown voltage of these valves but equals or exceeds the ionization voltage when the positionmined amount. Thus, when the positional disagreement is less than, this predetermined amount, the control connections between the coarse control system and the grids of valve 2| are interrupted and the coarse control system is ineffective, and when the disagreement equal or exceeds this amount, the valves become conducting and the voltage induced in the secondary winding of the transformer 3215 applied to the grids of the valve 2| and is thereafter eflective in controlling the valve 2|. Resistors 2i and 21 having relatively high ohmic resistances are included in the connections between the terminals of the secondary windings 28-, 26s and the grids 2|e and 2|: of valve 2|. These resistors SI and 31 assist the valves 33 and SI in transferring the control from the fine control system to the coarse control system when the positional disagreement equals or exceeds the predetermined amount mentioned in the foregoing description.

For the purpose of preventing hunting in the operation of the system, a capacitor 3' is connected in series withthe resistor 25 across the terminal of the driving motor l2. The charge on this capacitor 38 varies as the voltage of the armature varies. When the voltage of the motor armature is constant, the charge on the capacitor is constant and when the voltage of the motor is varying at a high rate, the charge on the capacitor 38 is likewise varying at a high rate. When the charge on the capacitor ll is varying, a current is caused to flow in the resistor 25 which is proportional to the rate at which the charge on the capacitor is varying. In other words, the current caused to flow in the resistor 25 is proportional to the rate of change of the charge on the capacitor which, in turn, varies in accordance with the rate of change of voltage of the motor armature i2 and since the voltage of the motor I2 is approximately proportional to its speed, the current caused to flow in the resistor 25 is also approximately proportional to the rate of change of the speed of the motor l2. Thus the capacitor introduces a correcting force or voltage into the grid circuit of the valve 2| which is proportional to the rate of change of speed of the motor |2. The polarity of the connections of the capacitor II in the grid circuit of the electric valve 2| is such that the current caused to flow in the resistor 25 as a result of a change in the charge on the capacitor 22 is in such a direction as to control the armature reaction generator 13 through valves 2|, Ii, and I6 transiently to reduce the amount of current that is supplied to the motor i2 so that the amount of current actually supplied to the motor i2 for any given positional disagreement oi the pilot device and driven object is less than would otherwise be supplied to the motor 2. In addition to the capacitor 38 a transformer 29 is provided for introducing another corrective force or component into the control to prevent hunting or overshooting. The secondary winding of this transformer 39 is connected in series relationship with the capacitor 38, and the primary winding of this transformer is connected across a resistor 40 which is connected in series relationship in the connections between the generator II and th motor |2 so that the voltage drop across resistor 40 is proportional to the current in the armature circuit of the motor. The resistor II is provided with a movable contact member 40- for properly proportioning the corrective component introduced through transformer II with respect to that produced by the capacitor 28. A voltage is induced in the secondary winding of transformer 39 only when the armature current of the motor I2 is changing and the magnitude of this induced voltage is proportional to the rate at which the armature current is changing. Consequently, the corrective component introduced by transformer 39 i proportional to the rate of change of armature current of motor l2, and since in a motor having constant excitation,

such as the motor l2, torque is proportional to current. the corrective component introduced by transformer I! is proportional to the rate of change of torque of motor l2.

with the foregoing understanding of the elements and their organization in the completed system, the operation of the system itself will readily be understood from the following detailed description:

Assuming the pilot device II and the driven object ID to be in positional agreement, the system is in its normal deenergized condition in which it is illustrated. As previously pointed out, .when in this condition, both paths of the valve 2| are conducting equal amounts of current and likewise, valves l5 and ii are conducting equal amounts of current so that the opposing control field windings He and Ila of the armature reaction generator are equally excited and the output voltage of the generator II is zero. Manual rotation of the pilot device effects a corresponding but multiplied rotation of the rotor of transmitter 21, causing a rotation of the magnetic field of the stator of receiver regulator 2| so that a voltage is induced in the rotor winding of the receiver regulator proportional to the amount of rotation of the pilot device II. This induced voltage is applied to the grid circuit oi the electric valve 2| and results in increasing the current flowing in one conducting path of the valve and decreasing the current flowing in the other path. Assuming that the direction of rotation of the pilot device is such as to increase the current flowing from the cathode to the anode 2|. and to decrease the current flowing from the cathode to the anode 2 lb, the negative bias of the grid of valve I5 is increased and the negative bias of the grid of valve I8 is decreased, owing to the increase and decrease in the voltage drops across the resistors l9 and 2|, respectively. As a result, the conductivity of valve It is increased and the conductivity of valve II is decreased, and

this results in increasing the excitation of the control field winding I3: and decreasing the excitation of the control field winding lie of the armature reaction generator ii. The difference in excitations of the two opposing field windings lie and [3a produces a net excitation along the control axis of the generator I3, and as a result, the generator It generates an output voltage which supplies current to the armature of the motor II in such a direction that the motor is caused to rotate in a direction to drive the object III toward correspondence with the pilot device Ii.

If the driven object l0 cannot follow the rapid movement of the pilot device H with the result that the positional disagreement of the driven obiect and pilot device equals or exceeds the predetermined amount, the voltage induced in the secondary winding of the transformer 32 becomes so great that the voltages applied to the electrode termindls of the electric valves 32 and 34 exceed the ionization voltages of these valves causing them to become conducting. Voltages continue i Thus when the electric valves assasco system and the electric valve 2| are completed and the control of the follow-up system is eflectively transferred from the high speed fine control system to the low speed coarse control system. The completion of the connections between the receiver regulator II and the grid circuit of the electric valve 2i causes such a high voltage to be applied to the grid circuit of the valve 2| that the current supplied by armature reaction generator it to the armature of motor l2 causes motor i2 to drive the driven object at maximum speed in the same direction as that in which the pilot device is moving.

Had the departure from correspondence been in the opposite direction, the operation of each of the elements would be similar but opposite to that of the operation thus far described with the result that current of opposite polarity would have been supplied to.the armature of the1rnotor l2 and the motor l2 would have driven the driven object in the reverse direction.

Assuming now that the pilot device is brought to rest, the driven object i will be approaching correspondence with the pilot device at maximum speed and when it arrives within the predeter- It so as to lower the voltage of the generator II a greater amount than it would otherwise be lowered if controlled solely by the decreasing voltage induced in the secondary winding of receiver regulator 28 as the system approaches correspondence. The lowering of the voltage of generator I! may reach such an extent that the generator voltage will be exceeded by the countervoltage of motor 12, thereby resulting in operation of motor I2 as a generator to pump current back to generator l2 and thereby to produce a strong andefl'ective braking torque of motor l2, such as to bring the motor and driven object ill to rest mined maximum permissible amount of position al disagreement with the pilot device, the voltag'es applied to the electrode terminals of valves 33 and 34 will become less than the ionization voltage of these valves and the valves will accordingly become non-conducting. The result of the valves 31 and 34 becoming n'onconducting is to interrupt the control connections between the low speed coarse control system and the grid circuit of the valve 2i, thereby to render the low speed coarse control system ineffective and to transfer the control to the high speed fine control system. Finally, as the driven object approaches exact and accurate correspondence with the pilot device Ii, theaxis of the rotor'winding of the receiver regulator 2| approaches a right angle relationship with the axis of the magnetic field of the stator winding and as a result the voltage induced in the rotor winding of the receiver regulator becomes zero and'the electric valve 2i is restored to the condition of equal conduction in both of its conducting paths. This results in disappearance of the net excitation along the control axis oi the armature reaction generator l3 so that its output voltage is reduced to zero and the motor I2 is brought to rest with the driven object it in correspondence with the pilot device H.

I As previously suggested, the operation of the system as described in the foregoing is modified slightly; especially during acceleration and 'deceleration, for the purpose of minimizing "overshooting" and "hunting."

During acceleration, the rising voltage of the motor terminals will begin to build up a charse on the capacitor 3| and the charging current of the capacitor will flow through the resistor 2| in the grid circuit of the electric valve 2| with the result that the bias voltages of the grids 2|. and 2i: are altered so that the current supplied to the motor 12 is reduced below the value that would otherwise be supplied to the motor for the then existing positional disagreement of the pilot device and driven object.

During deceleration of the motor, i. e., when the driven object is approaching correspondence with the pilot device, the capacitor 80 discharges and the fiow of discharge current through resistor 2! produces a voltage across the resistor which alters the bias voltages of the grids of valve without overshooting the position of correspondence.

If the deceleration of motor l2 from maximum speed is proceeding at an extremely rapid rate, the discharge current of the capacitor 38 will be correspondingly high, and the effect of this high discharge current through the resistor 25 on the bias voltages of the grids of valve 2| may be so pronounced as actually to decrease the voltage of generator I! to zero and to reverse it. This results in plugging" the motor l2 and causing it to exert an extremely strong and effective braking torque to decelerate the driven object to rest in correspondence with the ilot device without significant overshooting or hunting.

At very low speeds of motor l2 the terminal voltage and rates of change thereof are usually low in comparison with the motor current and rates of change thereof. Consequently, at these very low speeds, transformer 39 supplies the principal component of the antihunt correction and this component operatesin a manner similar to that produced by the capacitor 38 to produce the antihunt operation described in the foregoing. i

In certain follow-up applications the loads imposed on the follow-u motor are so heavy and the rates of acceleration and deceleration encountered are so high that the terminal voltage of the motor is not an accurate measure of-its speed. In order to provide accurate control for these applications and to obtain an antihunting eilect that is accurately proportional to the rate of change of speed of the motor, a tachometer generator I mechanically driven from the shaft of the follow-up motor 42 is provided, as illustrated in the modification of Fig. 2. In this modification, the follow-up motor 42 corresponds to the follow-up motor l2 of Fig. 1; The series eircuit comprising the secondary winding of transformer 43, capacitor 44, and resistor 45 is connected across the terminals of the tachometer generator ll instead of being connected across the terminals of the follow-up motor 42 as the corresponding series circuit is connected in the system of Fig. 1. Otherwise, the modification of Fig. 2 is identical with the system of Fig. 1 and the operation is also identical, with the exception that the accuracy is improved because the voltage supplied by the tachometer generator ll is an accurate measure of the speed of the followup motor 42.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form and the principle thereof has been described together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements and connections shown and described are merely illustrative and that the invention isnot limited thereto, since alterations and modifications will readily suggest themselves to persons 11 a skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent oi the United States is:

l. A follow-up control system for a pilot device and driven object comprising in combination, driving means for said object, means ior controlling said driving means comprising an electric valve provided with a control grid, coarse and fine control means responsive to positional disagreement 01 said pilot device and driven object for producing control voltages dependent on the positional disagreement of said pilot device and driven object, electrical connections from each 01 said control means to said grid, electric valve means having main discharge supporting anodes and cathodes included serially in the connections between said coarse control means and said grid, and responsive to a predetermined value of said control voltage of said coarse control means for conducting current from said coarse control means through the circuit 01 the connections of said fine control means thereby to render said fine control means inefiective and said coarse control means eiIective and responsive to values of said control voltage of said coarse control means less than said predetermined value ior interrupting the supply of current from said coarse control means to the circuit of said fine control means thereby to transfer control from one 01 said control means to the other in accordance with the magnitude of said positional dis agreement.

2. A follow-up control system comprising in combination, a pilot device, a driven object, electri valve means having a pair 0! conducting paths and control grids for controlling the conductivity of each of said paths, driving means for said object controlled by said valve means, fine and coarse control means for producing control voltages having predetermined relationships to positional disagreement of said pilot device and driven object, electrical connections including a transformer between said fine control means and said grids, electrical connections including a transformer between said coarse control means and said grids and electric valve means containing an ionizable medium and having their main discharge supporting anodes and cathodes serially included in the connections between said coarse control means and said grids and responsive to a predetermined voltage produced by said coarse control means for conducting current from said coarse control means through the circuit of the connections between said fine control means and said grid thereby to transfer control of said driving means from said fine control means to said coarse control means.

3. A follow-up control system comprising in combination, a pilot device, a driven object, electric valve means having a pair or conducting paths and control grids for controlling the conductivity oi each of said paths, driving means for said object controlled by said valve means, fine and coarse control means for supply voltages to said control grids having predetermined relationships to positional disagreement or said pilot device and driven object for controlling said driving means to drive said object toward correspondence with said pilot device, electrical connections between said coarse control means and said grids and electric valve means containing an ionizable medium and main discharge supporting anodes and cathodes connected serially in said connections and responsive to a predetermined voltage produced bysald coarse control means tor-conducting current from said coarse control means to the grid circuit or said first mentioned electric valve means thereby to transier control oi said driving means from said fine control means to said coarse control means.

4. A follow-up control'system comprising in combination, a pilot device, a driven object, electric valve means having a pair oi conducting paths and control grids for controlling the conductivity oi each of said paths, driving means (or said obiect controlled by said valve means, fine and coarse control meansior producing control voltages dependent upon the positional disagreement of said pilot device and driven obiect. a first control transiormer having its primary winding connected to said fine control means and its secondary winding connected to said grids for supplying the voltage irom said fine control means to said grids, a resistor included in circuit between each 0! said grids and a corresponding terminal oi said secondary winding. a second control transformer having its primary winding connected to said coarse control means and having connections from its secondary winding to the connection points 0! said resistors and said grids, an electric valve having its main discharge supporting cathode and anode serially included in each of said connections between the secondary winding of said second transformer and said grids and responsive to a predetermined voltage produced by said coarse control means for conducting current from the secondary winding of said second transiormer' through the secondary circuit of said first transiormer thereby to transier control of said driving means between said fine and coars control means in accordance with the positional disagreement oi said pilot device and driven object.

5. A rollowup control system for causing a driven object to iollow the movement of a pilot device comprising an electric motor for driving said object, an armature reaction generator provided with a pair oi opposed control field windings for su plyin said motor, electric valve means provided with a pair oi current conducting paths for controlling the excitation of said field windings, said valve means being provided with control grids for separately controlling the conductivity oi said paths, means responsive to positional disagreement oi said pilot device and driven object for supplying voltages to the grid circuit of said valve means to control said motor to drive said object toward correspondence with said pilot device. and antihuntlng means comprising a capacitor connected in said grid circuit and a tachometer generator driven by said motor for supplying a voltage to said capacitor proportional to the speed of said motor so that the grid voltage of said valve means is modified in accordance with the rate of change of speed of said motor.

8. A follow-up control system for causing a driven object to follow the movement of a pilot device comprising a direct current electric motor for driving said object, an armature reaction generator provided with a pair of opposed control field windings for supplying said motor, electric valve means provided with a pair of current conducting paths for controlling the excitation of said field windings, said valve means being provided with control grids for separately controlling the conductivity oi said paths, means responsive to positional disagreement oi said pilot 13 device and driven object for supplying voltages to the grid circuit of said valve means to control said motor to drive said object toward correspondence with said pilot device, and antihunting means comprising a capacitor connected in said grid circuit and a tachometer generator driven by said motor for supplying a voltage to said capacitor proportional to the speed of said motor thereby to modify the grid voltage of said valve means in accordance with the rate of change of speed of said motor and a transiormer having its secondary winding connected in series with said capacitor and having its primary winding connected to be energized by the armature current or said motor 50 that said grid voltage is further modified in accordance with the rate of change of torque of said motor.

MAR'IIN A. EDWARDS.

anrmucas crrnn The following references are of record in the me of this patent:

UNITED STATES PATENTS 

